Process for warm extrusion of metal



INVENTORS, Charles Ilrazinsn 'E er' at` cf M/-TIIu'ldar and A- n/y FiledMarch 9, 1956 C. G. GRAZIOSO ETAL PROCESS FOR WARM EXTRUSION 0F METALNov. 10, 1964 P/"zof 6r? exzrasz'on ai' room temperature Cf/,az slug "0engi/z [aims/2f Pfc/W@ and mdf/[36 H6321 .slug OZOOVe/aw /lql UnitedStates Patent C 3,156,043 PROCESS FOR WARM EXTRUSlN OF METAL Charles G.Grazioso, 2116 Hartel Ave., Philadelphia 15, Pa., and Gerard W. Mulder,RR. 2, Delavan, Wis. Filed Mar. 9, 1956, Ser. No. 570,645 1 Claim. (Cl.29--552.3) (Granted under Title 35, U.S. Code (1952), sec. 266) Theinvention described herein may be manufactured and used by or for theGovernment for governmental purposes without the payment of any royaltytherein.

This invention relates to a method of extruding metals and moreparticularly to the extrusion of a billet at a temperature in theVicinity of the critical point, Acl, of the metal to be worked.

Heretofore metal has been extruded cold, at room temperature, and hotwherein the metal to be worked is heated to a temperature substantiallyat the melting point thereof where the properties of the metal arethixatropic.

We have discovered that a number of important advantages can be gainedin the extrusion of high or low carbon ferrous ,metals and alloys, ornon-ferrous metals and alloys, if a billet to be extruded is changed inits physical properties and particularly in its response to physicalforces by being heated to a temperature below the critical point, Acl ofthe metal and then extruded.

Our process is to be distinguished from pre-heating in that thetemperatures used cause substantial physical changes in the metal overand above changes normally associated with pre-heating. However thetemperatures utilized are substantially below the temperature at themelting point of the metal to be worked as in hot forging or hotextrusion.

Our studies have shown that the property of flowability f metal is notdirectly proportional to temperature of the metal being extruded. Littleadvantage over cold extrusion, is noted in increasing the temperature ofa billet to be extruded above room temperature in the range of 400 F. Infact, little advantage has been noted in increasing the temperature of abillet to a point below 750 F. At temperatures above 75 0 F. thefiowability increases rapidly and this increase in flowability carrieson as the temperature is further increased. We prefer to heat the metalto within 200 F. of the critical point of the metal of the billet.

A metal billet extruded at a temperature in the range between 750 F. andwithin 200 F. of the critical point can be shaped in one extrusion anamount equal to three separate and distinct cold extrusions and manysmall products may be extruded at vthe low end of the temperature range.

A billet heated to a temperature in this range requires but one half toone third the press tonnage required in cold extrusion to cause themetal to ow; the number of unit extrusionsrequired will be decreased; inmany cases the need for auxiliary heat treatment or annealing isobviated, or at least materially reduced, thereby reducing capitalinvestment and fabrication costs.

An object of this invention, therefore, is to change the physicalproperties of a metal to be extruded by heating the metal above roomtemperature and below the critical point AC1.

3,156,043 Patented Nov. 10, 1964 ice critical point AC1 to completelycup the billet in one extrusion.

A further object of our invention is to heat a ferrous or non-ferrousbillet to a temperature within the range of 750 F. to within 200 F. ofthe critical point AC1 and vextrude the billet at a temperature withinsaid range.

A further object of this invention is to heat a low or high carbon steelbillet, or alloy thereof, to within 200 F. ofthe critical point AC1 ofthe billet and extrude the billet at that temperature.

A more specic object of our invention isv to heat a steel, or steelalloy billet to within 200 F. of the billet In the drawing,

FIGURE 1 shows a typical mill schedule for prior art cold extrusioncupping of an artillery shell;

FIGURE 2 shows a typical mill schedule for warm extrusion cupping of anartillery shell and FIGURE 3 shows an iron-carbon phase diagram illus'-trating the lower critical temperature and phase changes of steel onheating and cooling.

The following example is given by way of illustrating the method, andfurther advantages, of our invention.

A three inch round bar of W.D. 1018 steel is cut t0 a length equivalentto the weight of a finished mm. artillery shell which weighsapproximately 26 pounds. This billet was heated to 1250 F. in acontrolled atmosphere furnace. It was then placed in a 3000 tonhydraulic press. The die used was substantially equivalent to dies usedon the third successive cold extrusion when this shell is fabricated bycold extrusion. Hydraulic pressure was applied and the actual dialreading of the press reached a maximum of 890 tons. The iinal piece hadsize and shape substantially equivalent to that obtained on the thirdextrusion under cold extrusion methods.

To accomplish this same degree of metal ow under cold extrusion, threeindividual extrusions are required with press tonnages approximating2000 ton-s of the first press, 1500 tons on the second press, and 1200tons on the third press. Coupled with this it is necessary under coldextrusion methods to anneal the piece being Worked after each extrusionin order to permit reestablishment of grain size prior to additionalextrusion.

We have found that die life is substantially increased over the die lifeof cold extrusion methods. And since the temperatures are lower than thetemperatures used in hot extrusion we have found these dies to lastlonger than. Y

those used in hot extrusion methods. Further, in our process only onethird the number of dies, hydraulic or mechanical presses, and annealingequipment will be necessary on a production line making this process farmore economical as to first costs as Well as operating costs.

Studies have been made as to the most economical temperature at which toWarm Extrude metal. At temperatures above 750 F. the flowabilityincreases rapidly and this increase in owability carries on as thetemperature is further increased. We prefer to heat metal to within 200F. of the critical point of the metal, but in this range we find itnecessary to use controlled atmosphere furnaces to prevent oxideformations on the surface of the billet. Lower temperatures reduce thetendency to form oxides but require more press tonnage and result inmore operations to perform the same degree of Work.

The optimum temperature will vary depending upon the chemicalcomposition, size, shape and weight of the t end product. Many smallproducts may be extruded in one operation at the low end of thetemperature range, whereas the economy on large pieces requiringconsiderable extrusion may lie in the upper zone of our temperaturerange even though controlled atmosphere heating is required to preventoxide formations on the metal surfaces.

It is understood that the particular method above described is given byway of example only and that our invention may be variously practicedwithin the scope of the following claim.

We claim:

A process of forming high or low carbon steel or its alloys consistingof heating in a controlled atmosphere a 3 inch diameter billet of WD.1018 steel 0f a weight approximately the Weight of a finished product to1250" F.,

3 placing said billet in a fully cupped die, and fully cupping 2,667,390said billet in a single extrusion. 2,756,876 2,767,835 References Citedin the le of this patent 2,767,837 UNITED STATES PATENTS 5 2,767,838

1,968,442 Clark et al. July 31, 1934 2,183,358 Six Dec. 12, 19392,400,866 Kronwall May 21, 1946 page 349.

4 Watson et al Ian. 26, 1954 Watson etal July 31, 1956 Nachtman et alOct. 23, 1956 Nachtman Oct. 23, 1956 Nachtman Oct. 23, 1956 OTHERREFERENCES Metals Handbook, 1948 ed., A.S.M., page 7 and

